views: Make view::Views::GetPreferredSize() const.

ui/views/window/custom_frame_view.cc

Index: ui/views/window/custom_frame_view.cc
diff --git a/ui/views/window/custom_frame_view.cc b/ui/views/window/custom_frame_view.cc
index cfb34e66c53fe8cf746d21feaef3b633b479c027..d3513d9711c6f3a93ac00aede089539231e31830 100644
--- a/ui/views/window/custom_frame_view.cc
+++ b/ui/views/window/custom_frame_view.cc
@@ -221,12 +221,12 @@ void CustomFrameView::Layout() {
   LayoutClientView();
 }
 
-gfx::Size CustomFrameView::GetPreferredSize() {
+gfx::Size CustomFrameView::GetPreferredSize() const {
   return frame_->non_client_view()->GetWindowBoundsForClientBounds(
       gfx::Rect(frame_->client_view()->GetPreferredSize())).size();
 }
 
-gfx::Size CustomFrameView::GetMinimumSize() {
+gfx::Size CustomFrameView::GetMinimumSize() const {
   return frame_->non_client_view()->GetWindowBoundsForClientBounds(
       gfx::Rect(frame_->client_view()->GetMinimumSize())).size();
 }